Semiconductor solar cells are utilized to convert light energy to useable electrical power through the photovoltaic effect. Briefly, a typical semiconductor solar cell includes an interface between n-type and p-type transparent semiconductor materials. Light shining on the semiconductor materials adjacent to the interface creates hole-electron pairs in addition to those otherwise present, and the minority charge carriers migrate across the interface in opposite directions. There is no compensating flow of majority carriers, so that a net electrical charge results. A useful electrical current is then obtained in an external electrical circuit by forming ohmic contacts to the p-type and n-type materials on either side of the interface.
In general terms, a photovoltaic solar cell (or PV cell) is fabricated by depositing or attaching the appropriate semiconductor layers in the form of a typically thin wafer onto a supporting substrate, and then adding additional components to complete the cell. The individual PV cells are electrically connected together in parallel into large arrays to deliver power of the desired voltage and current. The ratio of power output to area of the solar cell array is an important design parameter, since the required power output could in principle be satisfied, for example, by larger numbers of low power density PV cells made of silicon or by smaller numbers of high power density solar cells made of gallium arsenide. Large numbers of PV cells require more supporting structure and area with solar access (such as the scarce area on rooftops) adding cost and complexity to PV system, and reducing the amount of energy which can be generated on a given site, such as a building or plot of land.
A number of the individual PV cells are generally connected together in an array, typically by fastening the PV cells to a support structure and then electrically interconnecting the cells into series and parallel arrangements, as necessary to meet the power requirements. This incentive for improved power output and area reduction is particularly pressing for crystalline PV cells such as mono-crystalline silicone solar cells, which have higher power output per unit area than thin-film PV cells, but continue to be at a disadvantage in cost per unit area, mainly because of their manufacturing requirements.